It is well known that stormwater gathers a variety of pollutants as it flows across the landscape and even through stormwater drainage systems. See, for example, http://cfpub.epa.gov/npdes/home.cfm?program_id=6 and http://www.epa.gov/owow_keep/NPS/index.html .
In NRDC v. County of Los Angeles, Ninth...